The present invention relates generally to broadband communications, and more particularly to a method and circuitry for implementing demodulator circuits.
There is a growing acceptance of video services, such as video on demand, and an anticipated deployment of home servers. As a result, broadband appliance manufacturers have an increasing need to support multiple simultaneous channels of digital content delivered over the cable system. This need includes other systems such as satellite and terrestrial TV systems. The ability to simultaneously demodulate potentially all of the channels viewed by a particular home can fundamentally change the viewing paradigm for video content from one that is driven by network schedules to one that is driven by consumers independent of networks.
FIG. 1 is a simplified high-level block diagram of a traditional multi-channel cable and satellite demodulator 100 of a type that is used in cable and satellite systems. A multi-channel RF input signal typically includes a plurality of RF channels, each characterized by a different carrier frequency and being modulated in accordance with desired information to be carried on that channel. Each channel's bandwidth is less than the spacing of the carrier frequencies. For example, carrier frequencies in the UHF band (300 MHz to 3 GHz) may be spaced at 6 MHz intervals. Included are receiver chains 102a, 102b, and 102c. Each chain includes a tuner 110, an analog-to-digital converter (ADC) 120 and a digital demodulator 130. Digital demodulator 130 includes a forward error correction (FEC) circuit (not explicitly shown).
The function of each tuner 110 is to select an RF channel falling within a specific frequency band. There is one tuner for each RF channel. The input RF signal for a tuner contains many or all RF channels. Each tuner then converts the frequency of its selected RF channel to a lower fixed frequency pass band for cable systems, or to baseband for satellite systems. Each ADC 120 then digitizes the selected RF signal. Then each digital demodulator 130 performs signal demodulation and outputs recovered digital bits with error indication signals.
Each RF channel requires one analog tuner and analog band-pass or low-pass filters. The problem with this approach is that the cost, power consumption, and complexity go up as the required number of RF channels goes up.